Acne can be divided into two categories: inflamed (papules, pustules and nodules) and non-inflamed (open and closed comedones). Left untreated, non-inflamed acne may progress to inflamed acne.
WHITE HEADS :
Acne whitehead is called a closed comedo. When pores get clogged completely, the hair follicle plugged up with sebum, keratin and bacteria substance giving rise to tiny white spots known as white heads.
BLACK HEADS :
Acne blackhead is called an open comedo. When the pores get partially clogged by excessive produced sebum and keratin plug, Oxygen in the air reacts with the sebum, keratin and bacterial substance that cause the plug to turn black after it oxidizes.
Headless tiny red bumps with inflammation are referred to as papules. Papules associated with acne indicate that the follicle or pore has become damaged, the pore wall has collapsed and white blood cells may be attacking an infection.
Pustules are variety or pimple inflammations with a red circular lining with white or yellow colored pus in the center. One should avoid pricking or breaking these pimples. They are prone to cause dark spots or scars all over the skin.
Nodule is a deeper and wider papule which is categorized in the severe acne activities. They are much larger than the above types of acnes, are painful, inflamed bumps, without pus and are hard to touch. Any attempt to pop a nodule can result in scarring.
Cystic acne is large, pus-filled lumps that have a similar appearance to boils. Never try to prick or break cysts as the bacteria can spread over to other unaffected regions on the skin and you are more likely to get more cysts and nodules. These are the most serious type of skin lesion caused by acne and have the greatest risk of causing permanent scarring. They are very painful to touch and you may need the help of a dermatologist.